The present disclosure relates to an image forming apparatus including a plurality of photosensitive drums along a transferring belt.
An image forming apparatus of a photographic manner includes a plurality of photosensitive drums along a transferring belt and includes a plurality of primary transferring parts with respect to the plurality of photosensitive drums, respectively. A surface of each photosensitive drum is electrically charged and exposed according to image data, and thereby, an electrostatic latent image is formed on the surface of each photosensitive drum. Further, a toner of each color is adhered to the electrostatic latent image, and accordingly, the electrostatic latent image is developed, and thereby, a toner image of each color is formed. The toner image of each color formed on each photosensitive drum is primarily transferred to the transferring belt by each primary transferring part to which a voltage of a reverse polarity of the toner has been applied, and thereby a full color toner image is formed.
In order to supply an optimal transfer current to each primary transferring part, it is necessary to apply a transfer voltage according to a resistance of a transferring member, such as a roller or a belt, constituting each primary transferring part. However, the transferring member, such as the roller or the belt, constituting each primary transferring part may be degraded due to a temperature change or a change with an elapse of time, and accordingly, a resistance value may be changed. Therefore, it is necessary to correct the transfer voltage in accordance with a change of the resistance value of each primary transferring part.
For example, an image forming apparatus includes: an image carrier having a surface on which a developer image is formed; an intermediate transferring body to which the developer image is transferred; and secondary transferring means transferring the developer image from the intermediate transferring body to a recording medium by applying a secondary transferring bias to a secondary transferring part. A volume resistance rate of the intermediate transferring body has a temperature dependency. Moreover, the image forming apparatus has temperature sensing means sensing a temperature of the intermediate transferring body. In addition, according to a temperature sensing result by the temperature sensing means, impedance (resistance value) of the secondary transferring part is sensed, and then, an applied voltage of the secondary transferring bias is controlled.
However, because detection of the resistance value of the transferring member takes time, a construction including a plurality of primary transferring parts for respective toner colors, such as a color printer, takes further time in order to measure the resistance value of each primary transferring part. In addition, if the transfer voltage is corrected in accordance with the change of the resistance value of each primary transferring part, furthermore time is taken. Thus, productivity of printing process utilizing the plurality of primary transferring parts may be impeded.